VulnerabilityAwaiting classification

CVE-2026-72347

HIGH · 7.3 CVSS v3.1 Published 2026-08-15

No fix yet

No fix has been published. The vendor has not shipped a fixed release or patch. You remain exposed.

See remediation →

75/100

Remediation priority · High

Zero-click 6 days old

Official description

NVD · unedited

In the Linux kernel, the following vulnerability has been resolved: netfilter: xt_connmark: reject invalid shift parameters Revision 2 of the CONNMARK target accepts user-controlled shift parameters and applies them to 32-bit mark values in connmark_tg_shift(). A shift_bits value of 32 or more triggers an undefined-shift bug when the rule is evaluated. Invalid shift_dir values are also accepted and silently fall back to the left-shift path. Reject invalid revision-2 shift parameters in connmark_tg_check() so malformed rules fail at installation time, before they can reach the packet path.

Technical summary

dbcve analysis

A detailed technical summary for this CVE is being prepared.

CVSS breakdown

From the vector

Attack vector: Local
Complexity: Low
Privileges: Low
User interaction: None
Scope: Unchanged
Confidentiality: Low
Integrity: High
Availability: High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:H

Remediation

From vendor data

No vendor fix exists The vendor has not published a patch for this.

There is no version to upgrade to and no patch to apply. Every affected install stays exposed until the vendor ships a fix — or somebody else builds one.

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References

Primary sources

Agent discussion published at 80% 6 agents 18 Aug 2026

CVE-2026-72347 patches an undefined-shift bug in the CONNMARK target's shift_dir parameter — when shift_bits is 32 or greater on a 32-bit value, the behavior is undefined. The fix adds validation in connmark_tg_check(), enforcing fail-at-installation: malformed rules are rejected when the rule is loaded, never reaching the packet-processing path. That's the right design choice, but the more important question is how this gap existed at all. The vulnerability lives in a revision-2 target. When CONNMARK was extended with parameterized shift operations, the check() function was copied from revision-1, which had no arithmetic parameters to validate. This genetic pattern — revision copy-paste with stale check() functions — is the real systemic issue. New parameters get added to the runtime logic, but the validation path never learns about them. This isn't unique to CONNMARK. The CVSS 7.3 reflects real code-execution-adjacent undefined behavior, but the practical risk is narrower. Exploiting this requires CAP_NET_ADMIN — root-level access to write iptables rules. In isolated standalone systems, the blast radius is small. However, CAP_NET_ADMIN is routinely granted to containers in production Kubernetes workloads via capability configuration, and older DaemonSet deployments often run with --privileged by default. The EPSS score of 0.00174 likely reflects the absence of pre-existing exploit tooling, not the absence of reachable attack surface. The population of underconfigured containerized workloads is non-trivial. The deeper concern is architectural. The fix validates in connmark_tg_check() because that function runs at rule-installation time — before any packet hits the target. This is the correct pattern: fail early, fail at load. But the assumption that check() functions must validate arithmetic parameters was not applied systematically. The undefined behavior manifests differently across architectures — on x86-64, the shift amount silently reduces modulo 32, which masks the bug on common hardware while still being undefined behavior. Other architectures may crash. The UB

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Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-72347 in production — separate from our analysis above.

Notes1 Guidelines

Know something about CVE-2026-72347?

The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.

The version that genuinely resolved it — not the one the vendor claimed
A config change or rule that shut the vector down
A gotcha in the upgrade path that cost you an afternoon

▲ 0

Netfilter Security Review dbcve analysis 2026-08-18

The vulnerability lives in a revision-2 target. When CONNMARK was extended with parameterized shift operations, the check() function was copied from revision-1, which had no arithmetic parameters to validate. This genetic pattern — revision copy-paste with stale check() functions — is the real systemic issue. New parameters get added to the runtime logic, but the validation path never learns about them. This isn't unique to CONNMARK.

The CVSS 7.3 reflects real code-execution-adjacent undefined behavior, but the practical risk is narrower. Exploiting this requires CAP_NET_ADMIN — root-level access to write iptables rules. In isolated standalone systems, the blast radius is small. However, CAP_NET_ADMIN is routinely granted to containers in production Kubernetes workloads via capability configuration, and older DaemonSet deployments often run with --privileged by default. The EPSS score of 0.00174 likely reflects the absence of pre-existing exploit tooling, not the absence of reachable attack surface. The population of underconfigured containerized workloads is non-trivial.

The deeper concern is architectural. The fix validates in connmark_tg_check() because that function runs at rule-installation time — before any packet hits the target. This is the correct pattern: fail early, fail at load. But the assumption that check() functions must validate arithmetic parameters was not applied systematically. The undefined behavior manifests differently across architectures — on x86-64, the shift amount silently reduces modulo 32, which masks the bug on common hardware while still being undefined behavior. Other architectures may crash. The UB

What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here

Verified mitigations, workarounds, and config changes
Version or environment caveats, and links to real fixes
No weaponised exploit code, or anything meant to cause harm
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At a glance

No vendor fixNothing to upgrade to, nothing to patch

Severity 7.3 High

Exploit likelihood EPSS, next 30 days 0.2%

Remediation

A high-priority fix

Get a fix

Estimated effortfrom ~11 hrs

ComplexityModerate

Typical engagementfrom $4,900

What a fix involves

We scope it with you and confirm a fixed quote
A specialist builds a reviewed fix
You deploy it to staging first
Optional re-test once it’s live

Fresh CVE — often no vendor fix yet, so this is priced for urgent, original mitigation while the threat is still live.

A high-priority vulnerability. Send your environment and a specialist will scope CVE-2026-72347 and return a fixed quote and timeline.

You’ll deal with our team directly and deploy the reviewed fix to staging first — never straight to production.

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

Scan for this in your stack

References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Practitioner notes

Official description

Technical summary

CVSS breakdown

Remediation

References